1. Field of the Invention
The present invention relates to attachment of a drive motor unit to a medical obstruction treatment device sub-assembly, and more particularly to a rotatable attachment mechanism for attaching a medical brush sub-assembly comprising a brush at the distal end of a brush drive shaft and enclosed within a brush delivery catheter, to a drive motor unit.
2. Description of the Background Art
Commonly assigned, U.S. Pat. No. 5,370,653 to Cragg, incorporated herein by reference in its entirety, discloses a thrombectomy system for dissolving a soft fibrinous obstruction, such as a recently formed thrombus, within a patient's vascular system, either in a patent vein or artery or in a vascular implant, e.g. an A/V graft. The thrombectomy system employs rotating brush bristles within the thrombus to separate the fibrin of the thrombus from blood cells while mixing the separated fibrin with a dissolving or thrombolytic agent, e.g. streptokinase or urokinase, that is introduced at the same time into the separated fibrin.
Commonly assigned U.S. Pat. No. 5,681,355 to Serra et al., incorporated herein by reference in its entirety, discloses a hollow lumen, thrombectomy brush and method of fabrication which allows for the brush to be introduced over a previously placed guidewire into a very small blood vessel. The miniaturized brush is provided with an elongated, flexible, rotatable brush or drive shaft adapted to be attached at its proximal end to a drive motor for rotating the shaft. The drive shaft is formed with a proximal elongated section formed of a hollow, thin wall tube having an inner lumen and an outer surface and a distal section. The brush is formed of brush filaments, each having first and second ends and a predetermined length between the first and second ends, entrapped in a winding interface between turns of the coiled wire and the outer wall of the hollow tube extension in an entrapment zone intermediate the first and second ends.
The inventive rotating brush described in the '653 patent has flexible brush bristles extending outward from a brush shaft or drive shaft distal end in all directions. The brush is attached to the elongated, flexible, rotatable drive shaft or brush shaft which is attached at its proximal end to a drive motor to impart rotary motion to the brush shaft and bristles. The system includes a brush delivery catheter adapted to be introduced and advanced through a patient's blood vessels until the distal end is positioned adjacent the soft fibrinous thrombus. Once the brush delivery catheter is positioned, the brush bristles and brush shaft are passed through the brush delivery catheter lumen and out its distal opening to place the brush in contact with the soft thrombus. The bristles are sufficiently resilient and dimensioned for allowing compression and passage out of and back into the distal opening of the brush delivery lumen and for mixing into and macerating the fibrin of the soft thrombus, without damaging a vessel wall.
In one embodiment described in the '653 patent, the brush shaft is hollow to define a brush shaft lumen and preferably is formed with a penetrable distal tip valve normally closing the distal end opening of the brush shaft lumen. The thrombolytic agent is optionally delivered through the brush shaft lumen and through side exit holes or ports into the region of the brush bristles. The brush shaft lumen allows the advancement of the brush over a previously introduced and positioned guidewire to a thrombus in a blood vessel or the lumen of a medical implant.
In another embodiment disclosed in the '653 patent, the brush drive shaft is solid, and the dissolving agent is introduced through the brush delivery catheter lumen alongside the drive shaft lumen while the brush drive shaft is rotated. The thrombolytic agent is emitted from the distal end opening of the brush delivery catheter lumen in the region of rotation of the brush bristles for dissolving the soft thrombus exposed by the rotating brush bristles.
The assignee of the '653 and '355 patents and the present application has implemented the solid drive shaft brush embodiment of the '653 patent in the Cragg Thrombolytic Brush.TM.. The Cragg Thrombolytic Brush.TM. is presently used in the lumen of an A/V graft implanted in a patient's vascular system for hemodialysis to dissolve thrombi that form therein. The Cragg Thrombolytic Brush.TM. is described and depicted in "The Thrombolytic Brush", by Andrew H Cragg, MD presented at The Second Mid-Atlantic Conference on Angio Access: Establishment and Maintenance of Dialysis and Venous Access, Williamsburg, Va. (pp. 162-165 of proceedings) in October 1996 and in product literature published by the assignee in 1997.
In the Cragg Thrombolytic Brush.TM. embodiment, the brush and brush drive shaft are enclosed within the brush delivery catheter as a sub-assembly that allows the brush to be garaged in the brush delivery catheter lumen as it is advanced to the graft lumen and to be advanced out of the catheter lumen distal end opening. The brush sub-assembly includes a Y-connector at the proximal end of the brush delivery catheter that has a Y-connector lumen that the brush drive shaft passes through. The Y-connector includes a side port coupled to an infusion port for allowing thrombolytic agent to be introduced into the Y-connector lumen and then distally down the annular space between the brush drive shaft and the brush delivery catheter lumen. The proximal end of the Y-connector includes a seal for sealing around the brush drive shaft to prevent leakage of the infused thrombolytic agent and a threaded luer connector having a proximal luer hub that fits into an annular recess in the housing of the drive motor unit.
An enlarged male shaft hub is formed at the proximal end of the brush drive shaft that is inserted axially through a central opening of the annular recess and into engagement with a female bore aligned with the central opening. The female bore is integrally formed within a driven gear that is rotated by a drive gear coupled with the drive motor. As the shaft hub is seated into the female bore, the brush sub-assembly and the drive motor unit are brought together to fit the luer hub proximal end into the annular recess of the drive motor unit. The drive motor unit and the hub are rotated with respect to one another to rigidly attach them together. The brush is ejected distally from the brush delivery catheter lumen.
At this point, the brush delivery catheter and brush drive shaft are extended through the patient's vascular system and it is undesirable to rotate them within the vascular system. It is therefore necessary to rotate the drive motor unit while holding the brush sub-assembly still in order the attach the luer lock elements together. It is not always possible to know in advance just how the drive motor unit will be aligned with respect to the side port of the Y-connector when the attachment is finished. Thus, the attachment process and any adjustment has to be done carefully and relatively slowly to arrive at a suitable final attachment orientation.
The drive motor unit is manually grasped by the physician during the medical procedure so that the button can be depressed to energize the motor and so that the motor and brush can be moved back and forth to position the brush in the graft lumen. The rigid attachment can cause the side port of the Y-connector to extend in an awkward direction. The threaded attachment of the male and female luer connector elements can limit the physician's ability to rotate the drive motor unit and the brush sub-assembly to a desired orientation. The tubing that is coupled between the side port and the infusion port coupled with a source of thrombolytic agent can become twisted.
Moreover, the use of the luer lock attachment does not always provide positive feedback that the attachment is correct which can result in imprecise longitudinal alignment of the brush sub-assembly with the drive motor unit. If only a few turns are engaged, the brush at the distal end of the brush drive shaft may be incompletely ejected from the brush delivery catheter or the shaft hub may be incompletely seated into the female chuck. Over tightening of the male and female luer attachment elements can also occur.
In addition, vibration of the drive motor unit when it is operated and manual twisting of drive motor unit and/or the brush sub-assembly can cause the luer lock attachment to loosen, requiring periodic tightening or re-attachment.
These problems are magnified in the context of use of a hollow lumen drive shaft that allows introduction of the brush drive shaft over a previously positioned guidewire as envisaged in one embodiment of the above-incorporated '653 patent. In that context, it is often desirable to connect and disconnect the brush sub-assembly from the drive motor unit. At times during a procedure, it is desirable to remove or insert a guidewire from or into the proximal end opening of the drive shaft lumen while it is separated from the drive motor unit requiring detachment and reattachment of the luer lock elements.
A need exists for a simpler and quicker attachment mechanism that provides repeatable and precise dimensional attachment, positive feedback of attachment, and also allows for rotation of the brush sub-assembly with respect to the drive motor unit to a convenient orientation for accommodating infusate tubing and equipment.